The acquired immune deficiency syndrome (AIDS) is characterized by a progressive depletion of CD4 lymphocytes. The causative agent of AIDS, the human immunodeficiency virus (HIV) is a cytopathic retrovirus. Although the mechanisms of CD4 cell loss in HIV-infected people remains unclear, recent data indicate the direct cell killing of infected cells by HIV itself is likely responsible. An accessory gene of HIV, the vpr gene, plays an important role in the cytopathic effect of HIV. In the presence of an intact vpr gene, cultures of infected cells are nearly completely killed, while cultures infected with a virus that has a mutated vpr gene survive and replicate with the same kinetics as uninfected cells. Those cells that survive infection with a wild-type virus contain vpr genes with mutations. Furthermore, expression of Vpr itself alters cell cycle progression by causing cells to accumulate in G2/M. Vpr also plays another role in the virus life-cycle by allowing the pre-integration complex to enter the nucleus of infected cells before mitosis. This property allows HIV to infect terminally differentiated macrophages, an important reservoir of virus in the body. In this application, we seek to understand the mechanism of action of Vpr. Ultimately, we hope to determine if Vpr plays a role in the decline of CD4 cells during AIDS progression. Specifically, we will use a genetic screen for vpr mutations as well as site-directed mutations to determine the correlation between the different functions of Vpr. This will allow us to make models of the roles of Vpr in HIV pathogenesis. We will also characterize the effects of Vpr and Vpx of HIV-2 on cell proliferation. Next, we will characterize the cell cycle stage(s) affected by Vpr, and analyze the relationship between normal cell cycle controls and Vpr function. We will then determine the effects of Vpr in primary cells, and specifically determine how Vpr influences the half-life of lymphocytes and macrophages. Finally, we will use a screen for suppressors of the toxic effects of Vpr in yeast to Identify host cell targets of Vpr. In this application, we seek to understand the mechanism of action of Vpr. Ultimately, we hope to determine if Vpr plays a role in the decline of CD4 cells during AIDS progression. Specifically, we will use a genetic screen for vpr mutations as well as site-directed mutations to determine the correlation between the different functions of Vpr. This will allow us to make models of the roles of Vpr in HIV pathogenesis. We will also characterize the effects of Vpr and Vpx of HIV-2 on cell proliferation. Next, we will characterize the cell cycle stage(s) affected by Vpr, and analyze the relationship between normal cell cycle controls and Vpr function. We will then determine the effects of Vpr in primary cells, and specifically determine how Vpr influences the half-life of lymphocytes and macrophages. Finally, we will use a screen for suppressors of the toxic effects of Vpr in yeast to Identify host cell targets of Vpr.